1. Field of Invention
This invention relates to the field of Positron Emission Tomography (PET), Computed Tomography (CT) and other related imaging devices. More specifically, the present invention is related to a patient bed for use in one or more such scanning devices which require the bed to be moved between successive scans, and in which the scans are to be used cooperatively to produce an image of the patient.
2. Description of the Related Art
In the field of medical imaging, it is well known that patients are positioned on a bed which is mechanically moved into position within a field of view of a plurality of detectors. Depending upon the type of scanner, two opposing banks of detectors or a continuous ring of detectors may be provided. A patient gantry is defined by the imaging device, the gantry being minimized in diameter in order to: minimize the cost related to the number of detectors and associated hardware; maximize the efficiency of the scan by placing the detectors as close to the patient as possible; and to minimize the overall size of the imaging device. While there are other reasons for minimizing the diameter of the patient gantry, the effect is a need for lying the patient on the bed and then inserting the bed and patient into the gantry. This is especially necessary in situations where the patient has limited mobility.
Accordingly, it is typical to lower the patient bed to a level at which the patient may comfortably be seated. The patient then reclines on the bed and is positioned for the scan. The bed is then raised to the appropriate height to be inserted into the gantry, and is then moved into the gantry. There are several common support structures for supporting the bed throughout these various positions. Illustrated in FIGS. 1 and 2 is a typical support configuration in which a rail bed 102 is disposed above a lifting mechanism 100. In the illustrated embodiment, the lifting mechanism 100 is a linkage that is pivotally mounted at each end, one to the rail bed 102 and the other to a rail base 104. A patient bed 106, or pallet, is slidably mounted on the rail bed 102. In use, the lifting mechanism 100 is lowered for loading the patient, raised to the required level for scanning, and the patient bed 106 is then extended to enter the imaging device gantry. As illustrated in FIG. 2, as the patient bed 106 is extended, the moment created by the weight of the patient and the patient bed 106 increases as it is extended, causing the distal end of the patient bed 106 to deflect downwardly. While exaggerated in the illustration, the bed deflection has been measured at up to 20 mm. Movement of the bed in both the horizontal and vertical directions is accomplished using components subject to wear, such as belt drives and screw drives.
In the illustration of FIGS. 3 and 4, another typical support configuration has the lifting mechanism disposed above the rail bed 102′. The rail bed 102′ is supported on the floor by feet or casters 108′. in this embodiment, the patient bed 106′ is lowered for loading the patient on the patient bed 106′ and raised for extending the patient into the imaging device gantry. In this embodiment, the lifting device 100′ is movable axially along the rail bed 102′. The weight of the patient, patient bed 106′ and lifting mechanism 100′ creates deflection of the rail bed 102′ as illustrated. In FIG. 3, at particular locations of the lifting mechanism 100′ along the rail bed 102′, the rail bed 102′ defines a concave deflection. When the lifting mechanism 100′ is moved to other locations, it is seen in FIG. 4 that the rail bed 102′ defines a convex configuration.
In the latter embodiment, the load of the patient bed 106′ is cantilevered from the lifting mechanism 100′ with no secondary support. As a result, the amplitude of vibration has been known to be excessive. As in the first prior art embodiment, movement of the bed in both the horizontal and vertical directions is accomplished using components subject to wear, such as belt drives and screw drives.
In either of these embodiments, as well as other conventional patient bed supports systems, the deflection resulting from the movement of the patient bed, whether through increased moments as a result of extending the bed, vibration of the bed as a result of movement along the rail bed, or any other change in elevation is detrimental, especially in the case of two imaging devices whose images must be correlated. Typically, as a result of a variation in elevation between scanners, vertical position correction software is required.